EP2728771A2 - Method of performing a random access process and wireless device using same - Google Patents

Method of performing a random access process and wireless device using same Download PDF

Info

Publication number
EP2728771A2
EP2728771A2 EP12824218.7A EP12824218A EP2728771A2 EP 2728771 A2 EP2728771 A2 EP 2728771A2 EP 12824218 A EP12824218 A EP 12824218A EP 2728771 A2 EP2728771 A2 EP 2728771A2
Authority
EP
European Patent Office
Prior art keywords
random access
access procedure
wireless device
pdcch
triggered
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP12824218.7A
Other languages
German (de)
French (fr)
Other versions
EP2728771A4 (en
Inventor
Joon Kui Ahn
Jin Min Kim
Hyun Woo Lee
Suck Chel Yang
Dong Youn Seo
Seung Hee Han
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LG Electronics Inc
Original Assignee
LG Electronics Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US201161522694P priority Critical
Application filed by LG Electronics Inc filed Critical LG Electronics Inc
Priority to PCT/KR2012/006367 priority patent/WO2013025009A2/en
Publication of EP2728771A2 publication Critical patent/EP2728771A2/en
Publication of EP2728771A4 publication Critical patent/EP2728771A4/en
Withdrawn legal-status Critical Current

Links

Images

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W74/00Wireless channel access, e.g. scheduled or random access
    • H04W74/08Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
    • H04W74/0833Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00Arrangements affording multiple use of the transmission path
    • H04L5/003Arrangements for allocating sub-channels of the transmission path
    • H04L5/0053Allocation of signaling, i.e. of overhead other than pilot signals
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W74/00Wireless channel access, e.g. scheduled or random access
    • H04W74/02Hybrid access techniques

Abstract

Provided are a method of performing a random access process and wireless device using same in a wireless communication system. A first random access process and a second random access process are triggered in one subframe, and a wireless device selects one of the first random access process and the second random access process. The wireless device transmits a random access preamble on the selected random access process from the one subframe to a base station.

Description

    Technical Field
  • The present invention relates to wireless communication, and more particularly, to a method of performing a random access procedure in a wireless communication system, and a wireless device using the method.
  • Background Art
  • Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a promising next-generation mobile communication standard. Recently, LTE-advanced (LTE-A) based on 3GPP TS release 10 supporting multiple carriers is under standardization.
  • Multiple carriers are supported starting from 3GPP LTE-A, and such a technique is called a carrier aggregation. One carrier corresponds to one cell, and as a result, a user equipment can receive a service from a plurality of serving cells in a multiple-carrier system.
  • A random access procedure is used to maintain an uplink time alignment between a base station and a user equipment or to deliver a scheduling request. In general, the random access procedure includes transmission of a random access preamble and reception of a random access response.
  • It has been conventionally considered that the random access procedure is performed only in one cell. However, with the introduction of a plurality of serving cells, there is a need to design a random access procedure performed in the plurality of serving cells.
  • DISCLOSURE OF THE INVENTION
  • The present invention provides a method of performing a random access when a plurality of random access procedures are triggered simultaneously, and a wireless device using the method.
  • In one aspect, there is provided a method of performing a random access procedure in a wireless communication system. The method may comprise: selecting one of a first random access procedure and a second random access procedure if the first random access procedure and the second random access procedure are triggered in a single subframe; and transmitting to a base station a random access preamble for the selected random access procedure in the single subframe.
  • The first random access procedure may be triggered by an order of the base station, and the second random access procedure may be triggered by a medium access control (MAC) layer.
  • The first random access procedure and the second random access procedure may be triggered in different serving cells
  • In onther aspect, there is provided a wireless device for performing a random access procedure in a wireless communication system. The wireless device may comprise: a radio frequency (RF) unit for transmitting and receiving a radio signal; and a processor operatively coupled to the RF unit, wherein the processor is configured to: select one of a first random access procedure and a second random access procedure if the first random access procedure and the second random access procedure are triggered in a single subframe; and transmit to a base station a random access preamble for the selected random access procedure in the single subframe.
  • A method of selectively performing a random access procedure is proposed when a plurality of random access procedures are triggered.
  • BRIEF DESCRIPTION OF THE DRAWINGS
    • FIG. 1 shows a structure of a downlink radio frame in 3rd generation partnership project (3GPP) long term evolution-advanced (LTE-A).
    • FIG. 2 shows an example of monitoring a physical downlink control channel (PDCCH).
    • FIG. 3 shows an example of multiple carriers.
    • FIG. 4 shows an example of cross-component carrier (CC) scheduling.
    • FIG. 5 is a flowchart showing a random access procedure in 3GPP LTE/LTE-A.
    • FIG. 6 shows an example of a random access response.
    • FIG. 7 shows an example of triggering a plurality of random access procedures.
    • FIG. 8 is a flowchart showing a method of performing a random access according to an embodiment of the present invention.
    • FIG. 9 is a block diagram showing a wireless communication system according to an embodiment of the present invention.
    MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS
  • A wireless device may be fixed or mobile, and may be referred to as another terminology, such as a user equipment (UE), a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device, etc. The wireless device may also be a device supporting only data communication such as a machine-type communication (MTC) device.
  • A base station (BS) is generally a fixed station that communicates with the wireless device, and may be referred to as another terminology, such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, etc.
  • Hereinafter, it is described that the present invention is applied according to a 3rd generation partnership project (3GPP) long term evolution (LTE) based on 3GPP technical specification (TS) release 8 or 3GPP LTE-advanced (LTE-A) based on 3GPP TS release 10. However, this is for exemplary purposes only, and thus the present invention is also applicable to various wireless communication networks.
  • FIG. 1 shows a structure of a downlink radio frame in 3GPP LTE-A. The section 6 of 3GPP TS 36.211 V10.2.0 (2011-06) "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 10)" may be incorporated herein by reference.
  • A radio frame includes 10 subframes indexed with 0 to 9. One subframe includes 2 consecutive slots. A time required for transmitting one subframe is defined as a transmission time interval (TTI). For example, one subframe may have a length of 1 millisecond (ms), and one slot may have a length of 0.5 ms.
  • One slot may include a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain. Since the 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink (DL), the OFDM symbol is only for expressing one symbol period in the time domain, and there is no limitation in a multiple access scheme or terminologies. For example, the OFDM symbol may also be referred to as another terminology such as a single carrier frequency division multiple access (SC-FDMA) symbol, a symbol period, etc.
  • Although it is described that one slot includes 7 OFDM symbols for example, the number of OFDM symbols included in one slot may vary depending on a length of a cyclic prefix (CP). According to 3GPP TS 36.211 V10.2.0, in case of a normal CP, one slot includes 7 OFDM symbols, and in case of an extended CP, one slot includes 6 OFDM symbols.
  • A resource block (RB) is a resource allocation unit, and includes a plurality of subcarriers in one slot. For example, if one slot includes 7 OFDM symbols in a time domain and the RB includes 12 subcarriers in a frequency domain, one RB can include 7×12 resource elements (REs).
  • A DL subframe is divided into a control region and a data region in the time domain. The control region includes up to first four OFDM symbols of a first slot in the subframe. However, the number of OFDM symbols included in the control region may vary. A physical downlink control channel (PDCCH) and other control channels are allocated to the control region, and a physical downlink shared channel (PDSCH) is allocated to the data region.
  • A UL subframe may be divided into a control region and a data region. The control region is a region to which a physical uplink control channel (PUCCH) carrying UL control information is allocated. The data region is a region to which a physical uplink shared channel (PUSCH) carrying user data is allocated.
  • Now, a DL control channel is described.
  • As disclosed in 3GPP TS 36.211 V10.2.0, examples of a physical control channel in 3GPP LTE/LTE-A include a physical downlink control channel (PDCCH), a physical control format indicator channel (PCFICH), and a physical hybrid-ARQ indicator channel (PHICH). In addition, a control signal transmitted in a physical layer may be a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a random access preamble.
  • The PSS is transmitted in last OFDM symbols of a 1st slot (or a 1st subframe (i.e., a subframe with an index 0) and an 11th slot (or a 6th subframe (i.e., a subframe with an index 5). The PSS is used to attain OFDM symbol synchronization or slot synchronization, and is in association with a physical cell identify (ID). A primary synchronization code (PSC) is a sequence used for the PSS. There are three PSCs in the 3GPP LTE. One of the three PSCs is transmitted using the PSS according to the cell ID. The same PSC is used for each of the last OFDM symbols of the 1st slot and the 11th slot.
  • The SSS includes a 1st SSS and a 2nd SSS. The 1st SSS and the 2nd SSS are transmitted in an OFDM symbol adjacent to an OFDM symbol in which the PSS is transmitted. The SSS is used to attain frame synchronization. The SSS is used to attain a cell ID together with the PSS. The 1st SSS and the 2nd SSS use different secondary synchronization codes (SSCs). If the 1st SSS and the 2nd SSS each include 31 subcarriers, sequences of two SSCs with a length of 31 are respectively used for the 1st SSS and the 2nd SSS.
  • The PCFICH transmitted in a first OFDM symbol of the subframe carries a control format indicator (CFI) regarding the number of OFDM symbols (i.e., a size of the control region) used for transmission of control channels in the subframe. A wireless device first receives the CFI on the PCFICH, and thereafter monitors the PDCCH.
  • Unlike the PDCCH, the PCFICH does not use blind decoding, and is transmitted by using a fixed PCFICH resource of the subframe.
  • The PHICH carries a positive-acknowledgement (ACK)/negative-acknowledgement (NACK) signal for an uplink hybrid automatic repeat request (HARQ). The ACK/NACK signal for uplink (UL) data on a PUSCH transmitted by the wireless device is transmitted on the PHICH.
  • A physical broadcast channel (PBCH) is transmitted in first four OFDM symbols in a second slot of a first subframe of a radio frame. The PBCH carries system information necessary for communication between the wireless device and a BS. The system information transmitted through the PBCH is referred to as a master information block (MIB). In comparison thereto, system information transmitted on the PDCCH is referred to as a system information block (SIB).
  • Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI may include resource allocation of the PDSCH (this is referred to as a downlink (DL) grant), resource allocation of a PUSCH (this is referred to as an uplink (UL) grant), a set of transmit power control commands for individual UEs in any UE group, and/or activation of a voice over Internet protocol (VoIP).
  • The 3GPP LTE/LTE-A uses blind decoding for PDCCH detection. The blind decoding is a scheme in which a desired identifier is de-masked from a cyclic redundancy check (CRC) of a received PDCCH (referred to as a candidate PDCCH) to determine whether the PDCCH is its own control channel by performing CRC error checking.
  • The BS determines a PDCCH format according to DCI to be transmitted to the UE, attaches a CRC to the DCI, and masks a unique identifier (referred to as a radio network temporary identifier (RNTI)) to the CRC according to an owner or usage of the PDCCH.
  • A control region in a subframe includes a plurality of control channel elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate depending on a radio channel state, and corresponds to a plurality of resource element groups (REGs). The REG includes a plurality of resource elements. According to an association relation of the number of CCEs and the coding rate provided by the CCEs, a PDCCH format and the number of bits of an available PDCCH are determined.
  • One REG includes 4 REs. One CCE includes 9 REGs. The number of CCEs used to configure one PDCCH may be selected from a set {1, 2, 4, 8}. Each element of the set {1, 2, 4, 8} is referred to as a CCE aggregation level.
  • The BS determines the number of CCEs used in transmission of the PDCCH according to a channel state. For example, a wireless device having a good DL channel state may use one CCE in PDCCH transmission. A wireless device having a poor DL channel state may use 8 CCEs in PDCCH transmission.
  • A control channel consisting of one or more CCEs performs interleaving on an REG basis, and is mapped to a physical resource after performing cyclic shift based on a cell identifier (ID).
  • FIG. 2 shows an example of monitoring a PDCCH. The section 9 of 3GPP TS 36.213 V10.2.0 (2011-06) may be incorporated herein by reference.
  • The 3GPP LTE uses blind decoding for PDCCH detection. The blind decoding is a scheme in which a desired identifier is de-masked from a CRC of a received PDCCH (referred to as a PDCCH candidate) to determine whether the PDCCH is its own control channel by performing CRC error checking. A wireless device cannot know about a specific position in a control region in which its PDCCH is transmitted and about a specific CCE aggregation or DCI format used for PDCCH transmission.
  • A plurality of PDCCHs may be transmitted in one subframe. The wireless device monitors the plurality of PDCCHs in every subframe. Monitoring is an operation of attempting PDCCH decoding by the wireless device according to a format of the monitored PDCCH.
  • The 3GPP LTE uses a search space to reduce a load of blind decoding. The search space may also be called a monitoring set of a CCE for the PDCCH. The wireless device monitors the PDCCH in the search space.
  • The search space is classified into a common search space and a UE-specific search space. The common search space is a space for searching for a PDCCH having common control information and consists of 16 CCEs indexed with 0 to 15. The common search space supports a PDCCH having a CCE aggregation level of {4, 8}. However, a PDCCH (e.g., DCI formats 0, 1A) for carrying UE-specific information may also be transmitted in the common search space. The UE-specific search space supports a PDCCH having a CCE aggregation level of {1, 2, 4, 8}.
  • Table 1 shows the number of PDCCH candidates monitored by the wireless device. [Table 1] Search Space Type Aggregation level L Size [In CCEs] Number of PDCCH candidates DCI formats UE-specific 1 6 6 0, 1, 1A, 1B, 1D, 2, 2A 2 12 6 4 8 2 8 16 2 Common 4 16 4 0, 1A, 1C, 3/3A 8 16 2
  • A size of the search space is determined by Table 1 above, and a start point of the search space is defined differently in the common search space and the UE-specific search space. Although a start point of the common search space is fixed irrespective of a subframe, a start point of the UE-specific search space may vary in every subframe according to a UE identifier (e.g., C-RNTI), a CCE aggregation level, and/or a slot number in a radio frame. If the start point of the UE-specific search space exists in the common search space, the UE-specific search space and the common search space may overlap with each other.
  • In a CCE aggregation level L∈ {1,2,3,4}, a search space S(L) k is defined as a set of PDCCH candidates. A CCE corresponding to a PDCCH candidate m of the search space S(L) k is given by Equation 1 below. L Y k + mod N CCE , k / L + i
    Figure imgb0001
  • Herein, i=0,1,...,L-1, m=0,...,M(L)-1, and NCCE,k denotes the total number of CCEs that can be used for PDCCH transmission in a control region of a subframe k. The control region includes a set of CCEs numbered from 0 to NCCE,k-1. M(L) denotes the number of PDCCH candidates in a CCE aggregation level L of a given search space.
  • If a carrier indicator field (CIF) is set to the wireless device, m'=m+M(L)ncif. Herein, ncif is a value of the CIF. If the CIF is not set to the wireless device, m'=m.
  • In a common search space, Yk is set to 0 with respect to two aggregation levels L=4 and L=8.
  • In a UE-specific search space of the aggregation level L, a variable Yk is defined by Equation 2 below. Y k = A Y k - 1 mod D
    Figure imgb0002
  • Herein, Y-1=nRNTI≠0, A=39827, D=65537, k=floor(ns/2), and ns denotes a slot number in a radio frame.
  • In 3GPP LTE/LTE-A, transmission of a DL transport block is performed in a pair of the PDCCH and the PDSCH. Transmission of a UL transport block is performed in a pair of the PDCCH and the PUSCH. For example, the wireless device receives the DL transport block on a PDSCH indicated by the PDCCH. The wireless device receives a DL resource assignment on the PDCCH by monitoring the PDCCH in a DL subframe. The wireless device receives the DL transport block on a PDSCH indicated by the DL resource assignment.
  • Now, a multiple carrier system is described.
  • A 3GPP LTE system supports a case in which a DL bandwidth and a UL bandwidth are differently configured under the premise that one component carrier (CC) is used. The 3GPP LTE system supports up to 20 MHz, and the UL bandwidth and the DL bandwidth may be different from each other. However, only one CC is supported in each ofUL and DL cases.
  • Spectrum aggregation (also referred to as bandwidth aggregation or carrier aggregation) supports a plurality of CCs. For example, if 5 CCs are assigned as a granularity of a carrier unit having a bandwidth of 20MHz, a bandwidth of up to 100MHz can be supported.
  • One DL CC or a pair of a UL CC and a DL CC may be mapped to one cell. Therefore, when a wireless device communicates with a BS through a plurality of DL CCs, it can be said that the wireless device receives a service from a plurality of serving cells.
  • FIG. 3 shows an example of multiple carriers.
  • Although three DL CCs and three UL CCs are shown herein, the number of DL CCs and the number of UL CCs are not limited thereto. A PDCCH and a PDSCH are independently transmitted in each DL CC. A PUCCH and a PUSCH are independently transmitted in each UL CC. Since three DL CC-UL CC pairs are defined, it can be said that the wireless device receives a service from three serving cells.
  • The wireless device may monitor the PDCCH in a plurality of DL CCs, and may receive a DL transport block simultaneously via the plurality of DL CCs. The wireless device may transmit a plurality of UL transport blocks simultaneously via a plurality of UL CCs.
  • It is assumed that a pair of a DL CC #1 and a UL CC #1 is a 1st serving cell, a pair of a DL CC #2 and a UL CC #2 is a 2nd serving cell, and a DL CC #3 is a 3rd serving cell. Each serving cell may be identified by using a cell index (CI). The CI may be cell-specific or UE-specific. Herein, CI=0, 1, 2 are assigned to the 1st to 3rd serving cells for example.
  • The serving cell may be classified into a primary cell and a secondary cell. The primary cell operates at a primary frequency, and is a cell designated as the primary cell when the wireless device performs an initial network entry process or starts a network reentry process or performs a handover process. The primary cell is also called a reference cell. The secondary cell operates at a secondary frequency. The secondary cell may be configured after a radio resource control (RRC) connection is established, and may be used to provide an additional radio resource. At least one primary cell is configured always. The secondary cell may be added/modified/released by using higher-layer signaling (e.g., RRC messages).
  • The CI of the primary cell may be fixed. For example, a lowest CI may be designated as a CI of the primary cell. It is assumed hereinafter that the CI of the primary cell is 0 and a CI of the secondary cell is allocated sequentially starting from 1.
  • The UE may monitor a PDCCH through a plurality of serving cells. However, even if there are N serving cells, the BS may be configured to monitor the PDCCH for M (M≤N) serving cells. In addition, the BS may be configured to preferentially monitor the PDCCH for L (L≤M≤N) serving cells.
  • The multiple carrier system can use two types of scheduling.
  • First, according to per-CC scheduling, PDSCH scheduling is performed only in each serving cell. A PDSCH of a primary cell is scheduled in a PDCCH of the primary cell, and a PDSCH of a secondary cell is scheduled in a PDCCH of the secondary cell. Accordingly, a PDCCH-PDSCH structure of the conventional 3GPP LTE may be directly used.
  • Second, according to cross-CC scheduling, a PDCCH of each serving cell may schedule not only its PDSCH but also a PDSCH of another serving cell.
  • A serving cell in which the PDCCH is transmitted is called a scheduling cell, and a serving cell in which the PDSCH to be scheduled is transmitted through the PDCCH of the scheduling cell is called a scheduled cell. The scheduling cell may also be called a scheduling CC, and the scheduled CC may also be called a scheduled CC. According to the per-CC scheduling, the scheduling cell and the scheduled cell are identical. According to the cross-CC scheduling, the scheduling cell and the scheduled cell may be identical or different.
  • For the cross-CC scheduling, a carrier indicator field (CIF) is introduced in DCI. The CIF includes a CI of a cell having a PDSCH to be scheduled. It can be said that the CIF indicates a CI of a scheduled cell. According to the per-CC scheduling, the CIF is not included in DCI of a PDCCH. According to the cross-CC scheduling, the CIF is included in the DCI of the PDCCH.
  • The BS may configure the per-CC scheduling or the cross-CC scheduling in a cell-specific or UE-specific manner. For example, the BS may configure the cross-CC scheduling to a specific UE by using a higher layer message such as an RRC message.
  • Even if there are a plurality of serving cells, the BS may monitor the PDCCH only in a specific serving cell to decrease a load of blind decoding. A cell activated to monitor the PDCCH is called an activated cell (or a monitoring cell).
  • FIG. 4 shows an example of cross-CC scheduling.
  • A UE detects a PDCCH 510. Then, on the basis of DCI on the PDCCH 510, the UE receives a DL transport block on a PDSCH 530. Even if the cross-CC scheduling is configured, a PDCCH-PDSCH pair in the same cell may be used.
  • The UE detects a PDCCH 520. Assume that a CIF included in DCI on the PDCCH 520 indicates a second serving cell. The UE receives a DL transport block on a PDSCH 540 of the second serving cell.
  • Now, a random access procedure is described.
  • FIG. 5 is a flowchart showing a random access procedure in 3GPP LTE/LTE-A.
  • A wireless device receives a root index and a physical random access channel (PRACH) configuration index from a BS. Each cell has 64 candidate random access preambles defined by a Zadoff-Chu (ZC) sequence. The root index is a logical index for generating the 64 candidate random access preambles by the wireless device.
  • The random access preamble is limited to a specific time and frequency resource for each cell. The PRACH configuration index indicates a specific subframe and preamble format capable of transmitting the random access preamble.
  • Table 2 below shows an example of the random access configuration disclosed in the section 5.7 of 3GPP TS 36.211 V8.7.0 (2009-05). [Table 2] PRACH configuration index Preamble format System frame number Subframe number 0 0 Even 1 1 0 Even 4 2 0 Even 7 3 0 Any 1 4 0 Any 4 5 0 Any 7 6 0 Any 1, 6
  • The wireless device transmits a randomly selected random access preamble to the BS (step S110). The wireless device selects one of the 64 candidate random access preambles. In addition, the wireless device selects a corresponding subframe by using the PRACH configuration index. The wireless device transmits the selected random access preamble in the selected subframe.
  • Upon receiving the random access preamble, the BS transmits a random access response (RAR) to the wireless device (step S120). The RAR is detected in two steps. First, the wireless device detects a PDCCH masked with a random access-RNTI (RA-RNTI). The wireless device receives the RAR included in a medium access control (MAC) protocol data unit (PDU) through a PDSCH indicated by the detected PDCCH.
  • FIG. 6 shows an example of a random access response (RAR).
  • The RAR may include a timing advance command (TAC), a UL grant, and a temporary C-RNTI.
  • The TAC is information indicating a time alignment value sent by a BS to a wireless device to maintain a UL time alignment. The wireless device updates UL transmission timing by using the time alignment value. When the wireless device updates the time alignment, a time alignment timer starts or restarts. The wireless device may perform UL transmission only when the time alignment timer is running.
  • The UL grant is a UL resource used in transmission of a scheduling message described below.
  • Referring back to FIG. 5, the wireless device transmits a scheduled message to the BS according to a UL grant included in the RAR (step S130).
  • Hereinafter, the random access preamble, the RAR, and the scheduled message may also be called messages M1, M2, and M3, respectively.
  • The random access procedure may be triggered by at least one of the followings.
  1. (1) Triggering by a MAC layer: The MAC layer of the wireless device may trigger the random access procedure to request UL scheduling. Hereinafter, the random access procedure triggered by the MAC layer is called a MAC-random access procedure.
  2. (2) Triggering by a PDCCH order: A BS may instruct the wireless device to start the random access procedure due to a cause of UL time alignment or the like. The random access procedure is triggered when a specific field masked with a C-RNTI and having a DCI format 1A is set to a specific value. The PDCCH order may enable per-CC scheduling or cross-CC scheduling. Hereinafter, a random access procedure triggered by an order of the BS is called a PDCCH-random access procedure. The PDCCH-random access procedure may transmit a randomly selected random access preamble, or may transmit a dedicated random access preamble.
  • In 3GPP LTE/LTE-A, there is a restriction in that the random access procedure is performed only through a primary cell even if the wireless device has a plurality of serving cells. Both of the MAC-random access procedure and the PDCCH-random access procedure are performed only in the primary cell.
  • However, if frequency bands of the plurality of serving cells are separated from one another, a primary cell and a second cell may have different frequency features, and thus a random access procedure for UL time alignment may also need to be performed in the secondary cell.
  • In addition, although it is assumed in 3GPP LTE/LTE-A that the plurality of serving cells are managed by one BS, it is also possible to consider a case where the plurality of serving cells are managed by a plurality of BSs. This implies that the wireless device has a plurality of MAC layers. When the plurality of MAC layers operate independently, there may be a case where a plurality of random access procedures are simultaneously triggered by the plurality of MAC layers in the same time point (i.e., the same subframe).
  • FIG. 7 shows an example of triggering a plurality of random access procedures.
  • In a subframe n, a PDCCH-random access procedure of a secondary cell is triggered in a primary cell by a PDCCH order 710. This is for a BS to acquire UL timing information of the secondary cell. The PDCCH-random access procedure starts in a first subframe n+k (k>=6). The subframe n+k is a UL subframe which satisfies a PRACH configuration. It is assumed herein that a first random access preamble 720 for the PDCCH-random access procedure is transmitted in a subframe n+8.
  • Meanwhile, in addition to the PDCCH-random access procedure, it is also assumed that a second random access preamble 730 for a MAC-random access procedure is transmitted for a scheduling request in the subframe n+8.
  • A plurality of serving cells and/or a plurality of MAC layers may lead to various situations in which transmission of a plurality of random access preambles starts in the same subframe.
  • The present invention proposes to perform one selected random access procedure even if the plurality of random access procedures are triggered in the same subframe as described above. In doing so, simultaneous transmission of the plurality of random access preambles can be avoided. This is because excessive UL transmit power is consumed to transmit the plurality of random access preambles, and implementation of the wireless device and the network may become complicated.
  • FIG. 8 is a flowchart showing a method of performing a random access according to an embodiment of the present invention.
  • In step S810, a wireless device selects one of a plurality of random access procedures triggered simultaneously. For example, a first random access procedure and a second random access procedure may be triggered in one subframe. Although it is considered hereinafter that two random access procedures are simultaneously triggered, the number of random access procedures to be triggered is not limited thereto.
  • The plurality of random access procedures to be triggered may be classified according to a triggering cause, a dedicated random access preamble assignment, a serving cell to be triggered, and a combination of them.
  • The first and second random access procedure may have different triggering causes. For example, the first random access procedure may be a PDCCH-random access procedure triggered by the aforementioned BS order, and the second random access procedure may be a MAC- random access procedure triggered by a MAC layer of the wireless device.
  • The first random access procedure may be a non-contention based random access procedure which uses a pre-assigned dedicated random access preamble, and the second random access procedure may be a contention based random access procedure which uses a randomly selected random access preamble. The PDCCH-random access procedure may be the non-contention based random access procedure or the contention based random access procedure. In addition, the MAC-random access procedure may be the non-contention based random access procedure or the contention based random access procedure.
  • The first and second random access procedure may be triggered in different serving cells. The serving cell to be triggered may include at least any one of a serving cell for transmitting a random access preamble and a serving cell for receiving a random access response. For example, the first random access procedure may be triggered in the secondary cell, and the second random access procedure may be triggered in the primary cell.
  • In step S820, the wireless device performs the selected random access procedure. Assume that the first random access procedure is selected between the first random access procedure and the second random access procedure. The wireless device may transmit a random access preamble for the first random access procedure to the BS in the aforementioned single subframe.
  • Now, a criterion of selecting one of a plurality of random access procedures triggered simultaneously is described.
  • For clarity, it is assumed that two random access procedures are triggered simultaneously. Herein, a first random access procedure is a PDCCH-random access procedure, and a second random access procedure is a MAC-random access procedure. However, this is for exemplary purposes only, and thus there is no restriction on the number of random access procedures to be triggered or a triggering cause.
  • In a first embodiment, the MAC-random access procedure may be discarded (or stopped), and only the PDCCH-random access procedure may be performed.
  • Since a BS intends to acquire UL timing information of a corresponding cell through a PDCCH order, the PDCCH-random access procedure is assigned a higher priority than the MAC-random access procedure. This is because, even if the wireless device give up to perform the MAC-random access procedure for a scheduling request, a buffer status report (BSR) can be transmitted through scheduled PUSCH transmission.
  • In a second embodiment, the MAC-random access procedure may be delayed, and the PDCCH-random access procedure may be first performed.
  • Assume that a PDCCH order is received in a subframe n, and a random access preamble for the PDCCH-random access procedure is transmitted in a subframe n+k (k>=6). The subframe n+k is a first subframe which satisfies a random access configuration. In this case, even if the MAC-random access procedure is triggered in the subframe n+k, a random access preamble for the MAC-random access procedure is not transmitted. The random access preamble for the MAC-random access procedure may be transmitted in a first subframe which satisfies the random access configuration after the subframe n+k.
  • Alternatively, the random access preamble for the MAC-random access procedure may be transmitted in the first subframe which satisfies the random access configuration after the PDCCH-random access procedure is complete. Herein, the 'after the PDCCH-random access procedure is complete' may imply 'after an M2 message is received' or 'after an M3 message is transmitted'. This is to avoid unnecessary overlapping of the random access procedures.
  • In doing so, there may be an advantage when the plurality of random access procedures are triggered in a plurality of MAC layers. This is because delaying may be more effective in terms of buffer management than discarding a random access procedure having a low priority.
  • In a third embodiment, the PDCCH-random access procedure may be discarded (or stopped), and only the MAC-random access procedure may be performed.
  • The MAC-random access procedure triggered by the MAC layer of the wireless device is necessary to perform direct data communication. Therefore, an increase in a latency for a case of performing data communication may have a greater effect to a user than an increase in a latency for a case of acquiring UL timing. Accordingly, the MAC-random access procedure may be assigned a higher priority than the PCCH-random access procedure.
  • If the random access preamble for the PDCCH-random access procedure is not received in a corresponding subframe, the BS may transmit a new PDCCH order to the wireless device.
  • In a fourth embodiment, the PDCCH-random access procedure may be delayed, and the MAC-random access procedure may be first performed.
  • Assume that a PDCCH order is received in a subframe n, and the PDCCH-random access procedure is triggered in a subframe n+k (k>=6). The subframe n+k is a first subframe which satisfies a random access configuration. In this case, even if the PDCCH-random access procedure is triggered in the subframe n+k, if the MAC-random access procedure is triggered, a random access preamble for the MAC-random access procedure is transmitted in the subframe n+k. Subsequently, the wireless device may transmit a random access preamble for the PDCCH-random access procedure in a first subframe which satisfies the random access configuration after the subframe n+k.
  • Alternatively, the random access preamble for the PDCCH-random access procedure may be transmitted in the first subframe which satisfies the random access configuration after the MAC-random access procedure is complete. Herein, the 'after the MAC-random access procedure is complete' may imply 'after an M2 message is received' or 'after an M3 message is transmitted'. This is to avoid unnecessary overlapping of the random access procedures.
  • If the random access preamble for the PDCCH-random access procedure is a dedicated random access preamble, the BS may assign the dedicated random access preamble by considering the delay of the PDCCH-random access procedure.
  • In the aforementioned embodiment, the 'simultaneous' triggering of the plurality of random access procedures implies that a transmission time of the plurality of random access preambles overlaps partially or entirely.
  • When it is said that the PDCCH-random access procedure and the MAC-random access procedure are triggered simultaneously, it may include a case where the MAC-random access procedure is triggered before a corresponding random access preamble is received after a PDCCH order is received. For example, assume that the PDCCH order is received in a subframe n, and a PDCCH-random access procedure is triggered in a subframe n+k (k>=6). When the MAC-random access procedure is triggered in a subframe n+4, one of the aforementioned first to fourth embodiments may be applied.
  • The PDCCH-random access procedure may include a random access procedure which is triggered by using various mechanisms as well as by the PDCCH order. The MAC-random access procedure may include a random access procedure triggered by the wireless device autonomously as well as by the MAC layer.
  • The PDCCH-random access procedure and the MAC-random access procedure may be related to a serving cell to be triggered. For example, the PDCCH-random access procedure may include a random access procedure triggered by the BS in a secondary cell. The MAC-random access procedure may include a random access procedure triggered by the wireless device in a primary cell.
  • The PDCCH-random access procedure may include a non-contention based random access procedure, and the MAC-random access procedure may include a contention based random access procedure.
  • FIG. 9 is a block diagram showing a wireless communication system according to an embodiment of the present invention.
  • A BS 50 includes a processor 51, a memory 52, and a radio frequency (RF) unit 53. The memory 52 is coupled to the processor 51, and stores a variety of information for driving the processor 51. The RF unit 53 is coupled to the processor 51, and transmits and/or receives a radio signal. The processor 51 implements the proposed functions, procedures, and/or methods. In the aforementioned embodiment, an operation of the BS may be implemented by the processor 51.
  • A wireless device 60 includes a processor 61, a memory 62, and an RF unit 63. The memory 62 is coupled to the processor 61, and stores a variety of information for driving the processor 61. The RF unit 63 is coupled to the processor 61, and transmits and/or receives a radio signal. The processor 61 implements the proposed functions, procedures, and/or methods. In the aforementioned embodiment, an operation of the wireless device may be implemented by the processor 61.
  • The processor may include an application-specific integrated circuit (ASIC), a separate chipset, a logic circuit, and/or a data processing unit. The memory may include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and/or other equivalent storage devices. The RF unit may include a base-band circuit for processing a radio signal. When the embodiment of the present invention is implemented in software, the aforementioned methods can be implemented with a module (i.e., process, function, etc.) for performing the aforementioned functions. The module may be stored in the memory and may be performed by the processor. The memory may be located inside or outside the processor, and may be coupled to the processor by using various well-known means.
  • Although the aforementioned exemplary system has been described on the basis of a flowchart in which steps or blocks are listed in sequence, the steps of the present invention are not limited to a certain order. Therefore, a certain step may be performed in a different step or in a different order or concurrently with respect to that described above. Further, it will be understood by those ordinary skilled in the art that the steps of the flowcharts are not exclusive. Rather, another step may be included therein or one or more steps may be deleted within the scope of the present invention.
  • Claims (14)

    1. A method of performing a random access procedure in a wireless communication system, the method comprising:
      selecting one of a first random access procedure and a second random access procedure if the first random access procedure and the second random access procedure are triggered in a single subframe; and
      transmitting to a base station a random access preamble for the selected random access procedure in the single subframe.
    2. The method of claim 1, wherein the first random access procedure is triggered by an order of the base station, and the second random access procedure is triggered by a medium access control (MAC) layer.
    3. The method of claim 2, wherein the first random access procedure and the second random access procedure are triggered in different serving cells.
    4. The method of claim 3, wherein the selected random access procedure is the first random access procedure.
    5. The method of claim 4, further comprising, after transmitting the random access preamble for the selected random access procedure to the base station, transmitting a random access preamble for the second random access procedure to the base station.
    6. The method of claim 4, wherein the performing of the second random access procedure is discarded.
    7. The method of claim 2, wherein the first random access procedure is triggered when specific fields in control information regarding a control channel and received from the base station are set to a specific value.
    8. The method of claim 1, wherein the first random access procedure is a non-contention based random access procedure, and the second random access procedure is a contention based random access procedure.
    9. The method of claim 1, wherein the first random access procedure and the second random access procedure are triggered in different MAC layers.
    10. A wireless device for performing a random access procedure in a wireless communication system, the wireless device comprising:
      a radio frequency (RF) unit for transmitting and receiving a radio signal; and
      a processor operatively coupled to the RF unit, wherein the processor is configured for:
      select one of a first random access procedure and a second random access procedure if the first random access procedure and the second random access procedure are triggered in a single subframe; and
      transmit to a base station a random access preamble for the selected random access procedure in the single subframe.
    11. The wireless device of claim 10, wherein the first random access procedure is triggered by an order of the base station, and the second random access procedure is triggered by a medium access control (MAC) layer.
    12. The wireless device of claim 11, wherein the first random access procedure and the second random access procedure are triggered in different serving cells.
    13. The wireless device of claim 12, wherein the selected random access procedure is the first random access procedure.
    14. The wireless device of claim 10, wherein the first random access procedure is a non-contention based random access procedure, and the second random access procedure is a contention based random access procedure.
    EP12824218.7A 2011-08-12 2012-08-10 Method of performing a random access process and wireless device using same Withdrawn EP2728771A4 (en)

    Priority Applications (2)

    Application Number Priority Date Filing Date Title
    US201161522694P true 2011-08-12 2011-08-12
    PCT/KR2012/006367 WO2013025009A2 (en) 2011-08-12 2012-08-10 Method of performing a random access process and wireless device using same

    Publications (2)

    Publication Number Publication Date
    EP2728771A2 true EP2728771A2 (en) 2014-05-07
    EP2728771A4 EP2728771A4 (en) 2015-03-11

    Family

    ID=47715568

    Family Applications (1)

    Application Number Title Priority Date Filing Date
    EP12824218.7A Withdrawn EP2728771A4 (en) 2011-08-12 2012-08-10 Method of performing a random access process and wireless device using same

    Country Status (4)

    Country Link
    US (1) US9265069B2 (en)
    EP (1) EP2728771A4 (en)
    KR (1) KR101530808B1 (en)
    WO (1) WO2013025009A2 (en)

    Cited By (2)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    WO2016168024A1 (en) * 2015-04-14 2016-10-20 Qualcomm Incorporated Random access for low latency wireless communications
    EP3073649A4 (en) * 2013-11-19 2017-07-12 LG Electronics Inc. Method for performing random access procedure

    Families Citing this family (16)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    US8395985B2 (en) 2011-07-25 2013-03-12 Ofinno Technologies, Llc Time alignment in multicarrier OFDM network
    US9237537B2 (en) * 2012-01-25 2016-01-12 Ofinno Technologies, Llc Random access process in a multicarrier base station and wireless device
    US8995405B2 (en) 2012-01-25 2015-03-31 Ofinno Technologies, Llc Pathloss reference configuration in a wireless device and base station
    WO2013151651A1 (en) 2012-04-01 2013-10-10 Dinan Esmael Hejazi Cell group configuration in a wireless device and base station with timing advance groups
    US20130258956A1 (en) 2012-04-01 2013-10-03 Esmael Hejazi Dinan Random Access Process in a Wireless Device
    US8964593B2 (en) 2012-04-16 2015-02-24 Ofinno Technologies, Llc Wireless device transmission power
    US9210664B2 (en) 2012-04-17 2015-12-08 Ofinno Technologies. LLC Preamble transmission in a wireless device
    US8964683B2 (en) 2012-04-20 2015-02-24 Ofinno Technologies, Llc Sounding signal in a multicarrier wireless device
    US8971298B2 (en) 2012-06-18 2015-03-03 Ofinno Technologies, Llc Wireless device connection to an application server
    US9084228B2 (en) 2012-06-20 2015-07-14 Ofinno Technologies, Llc Automobile communication device
    US9210619B2 (en) 2012-06-20 2015-12-08 Ofinno Technologies, Llc Signalling mechanisms for wireless device handover
    US9179457B2 (en) 2012-06-20 2015-11-03 Ofinno Technologies, Llc Carrier configuration in wireless networks
    US9113387B2 (en) 2012-06-20 2015-08-18 Ofinno Technologies, Llc Handover signalling in wireless networks
    US9609499B2 (en) * 2013-05-22 2017-03-28 Avago Technologies General Ip (Singapore) Pte. Ltd. Apparatus and method to prioritize a random access procedure for emergency access
    US20150245252A1 (en) * 2014-02-26 2015-08-27 Qualcomm Incorporated High speed inter-radio access technology handover
    US20180302924A1 (en) * 2015-10-26 2018-10-18 Lg Electronics Inc. Method for performing random access in wireless lan system and apparatus therefor

    Family Cites Families (14)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    EP2198536A2 (en) 2007-10-08 2010-06-23 Lg Electronics Inc. Method of transmitting control signals in wireless communication system
    KR101461939B1 (en) 2007-11-14 2014-11-14 엘지전자 주식회사 Method for random access based on priority
    KR100925450B1 (en) 2008-03-03 2009-11-06 엘지전자 주식회사 Method for resolving collision of unlink signal
    KR101548748B1 (en) 2008-08-07 2015-09-11 엘지전자 주식회사 A method of random access procedure
    KR101539775B1 (en) 2009-01-08 2015-07-30 엘지전자 주식회사 Method for relaying data in wireless communication system based on tdd
    KR101485807B1 (en) * 2009-04-01 2015-01-28 삼성전자주식회사 A method for random access in a wireless communication system and an apparatus thereof
    KR101637004B1 (en) * 2009-04-23 2016-07-07 인터디지탈 패튼 홀딩스, 인크 Method and apparatus for random access in multicarrier wireless communications
    KR101294401B1 (en) 2009-10-12 2013-08-16 한국전자통신연구원 Method and system for random access in small cell of 3gpp lte-advanced system
    US8917593B2 (en) * 2010-03-18 2014-12-23 Qualcomm Incorporated Random access design in a multiple component carrier communication network
    KR101776873B1 (en) * 2011-01-11 2017-09-11 삼성전자 주식회사 Method and apparatus for setting uplink transmission power in mobile communication system
    US9398551B2 (en) * 2011-04-01 2016-07-19 Intel Corporation Performing multiple timing advance adjustments in a carrier aggregation communication system
    US20120300714A1 (en) * 2011-05-06 2012-11-29 Samsung Electronics Co., Ltd. Methods and apparatus for random access procedures with carrier aggregation for lte-advanced systems
    WO2013006111A1 (en) * 2011-07-06 2013-01-10 Telefonaktiebolaget L M Ericsson (Publ) Random access with primary and secondary component carrier communications
    US8395985B2 (en) * 2011-07-25 2013-03-12 Ofinno Technologies, Llc Time alignment in multicarrier OFDM network

    Cited By (6)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    EP3073649A4 (en) * 2013-11-19 2017-07-12 LG Electronics Inc. Method for performing random access procedure
    US10009932B2 (en) 2013-11-19 2018-06-26 Lg Electronics Inc. Method for performing random access procedure
    US10327266B2 (en) 2013-11-19 2019-06-18 Lg Electronics Inc. Method for performing random access procedure
    EP3627954A1 (en) * 2013-11-19 2020-03-25 LG Electronics Inc. Method for performing randomg access procedure
    WO2016168024A1 (en) * 2015-04-14 2016-10-20 Qualcomm Incorporated Random access for low latency wireless communications
    US10433339B2 (en) 2015-04-14 2019-10-01 Qualcomm Incorporated Random access for low latency wireless communications

    Also Published As

    Publication number Publication date
    KR101530808B1 (en) 2015-06-25
    KR20140085380A (en) 2014-07-07
    US20140161089A1 (en) 2014-06-12
    WO2013025009A2 (en) 2013-02-21
    WO2013025009A3 (en) 2013-05-30
    US9265069B2 (en) 2016-02-16
    EP2728771A4 (en) 2015-03-11

    Similar Documents

    Publication Publication Date Title
    US10165602B2 (en) Method for transmitting signal for MTC and apparatus for same
    JP6542449B2 (en) Method of configuring and scheduling partial subframes in a radio access system supporting an unlicensed band, and apparatus supporting the same
    EP3210320B1 (en) Method for transmitting and receiving data in wireless communication system and apparatus for the same
    US10448373B2 (en) Method for transmitting signal for MTC and apparatus for same
    US20180048437A1 (en) Method for setting starting position of data channel in wireless communication system and device using method
    CN106537995B (en) Method and user equipment for transmitting uplink signal, and method and base station for receiving uplink signal
    US10172152B2 (en) Method and apparatus for device-to-device UE for transceiving signal in wireless communication system
    KR102082971B1 (en) Method and apparatus for enhancing coverage of machine type communication (mtc) devices
    US10009882B2 (en) Method for receiving system information by MTC device located in cell coverage-expanded area
    US20190150130A1 (en) Method and apparatus for transceiving wireless signal in wireless communication system
    EP2949062B1 (en) Method and apparatus for performing a measurement to discover small cells in wireless communication system
    US10623967B2 (en) Method and MTC device for performing random access procedure for coverage enhancement
    US20200029290A1 (en) Method for transmitting/receiving synchronization signal for d2d communication in wireless communication system, and apparatus therefor
    US20180249509A1 (en) Method and apparatus for performing random access procedure in nb-iot carrier in wireless communication system
    EP3247163B1 (en) Method and user equipment for sending uplink signal, and method and base station for receiving uplink signal
    US20180287845A1 (en) Method and user equipment for receiving downlink signals, and method and base station for transmitting downlink signals
    US20190260550A1 (en) Method and apparatus for receiving ack/nack in wireless communication system
    KR101306404B1 (en) Method for uplink transmission and wireless device using the same
    US9544932B2 (en) Method and device for transmitting and receiving signal for device-to-device communication in wireless communication system
    EP3407525B1 (en) Method and device for setting a control channel and a data channel in a wireless communication system
    EP3128797A1 (en) Method for transmitting/receiving downlink control information in wireless communication system supporting device-to-device communication and apparatus therefor
    US10225827B2 (en) Method and apparatus for performing random access
    US10616872B2 (en) Method and apparatus for transmitting data in wireless communication system
    US10652872B2 (en) Downlink control information receiving method and user equipment, and downlink control information transmitting method and base station
    JP6509853B2 (en) How to perform a random access procedure

    Legal Events

    Date Code Title Description
    17P Request for examination filed

    Effective date: 20140131

    AK Designated contracting states

    Kind code of ref document: A2

    Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

    DAX Request for extension of the european patent (to any country) (deleted)
    A4 Supplementary search report drawn up and despatched

    Effective date: 20150209

    RIC1 Information provided on ipc code assigned before grant

    Ipc: H04W 74/08 20090101AFI20150203BHEP

    Ipc: H04B 7/26 20060101ALI20150203BHEP

    17Q First examination report despatched

    Effective date: 20161114

    18D Application deemed to be withdrawn

    Effective date: 20190711